Since the bran layer (the aleurone layer and all the outer part) of rice is hard, when brown rice as such is cooked in the usual manner, water can hardly penetrate into the interior of the rice grain, so that there is formed half-cooked rice which is hard on account of the fact that the gelatinization cannot completely reach the endosperm. Accordingly, rice is usually cooked in the form of polished rice in which the bran layer has been removed.
However, since the bran layer of rice contains abundantly vitamins, minerals, and fibrous material, it is desirable to use brown rice as such for food, and thus various methods for cooking rice have been developed, such as the method using an autoclave, the method of reboiling, or similar special methods. However, when using an autoclave, procedures such as adjusting the pressure or controlling the fire, etc. are not easy, and moreover, the loss of the nutrient ingredients may not be ignored, while the method of reboiling not only requires much labor and time but also damages the nutrient ingredients.
Thus, any of the methods of cooking brown rice, which have heretofore been employed, is not desirable, and actually these methods are not utilized much. Especially for the reason that these methods are unsuitable for daily practice in the home, brown rice is rarely consumed.
It is known however that even in such brown rice, if the hard bran layer is fissured, moisture can readily penetrate into the endosperm so that cooking is also readily achieved, and therefore, some methods of developing fissures in the bran layer of brown rice have heretofore been proposed.
One of the most suitable among them is a method in which brown rice is treated in such a manner that immediately after it has been heated while it is in a fluidized state by virture of hot air it is cooled (Japanese Pat. No. 1077284). This method provides brown rice in uniform quality of which the bran layers of all the rice grains have uniformly several streaks of fissure, brown rice, even when cooked in the usual manner like polished rice, makes nice cooked rice since moisture penetrates through the fissures into the endosperm until the interior of the rice grain is thoroughly gelatinized. Also this treated brown rice can be cooked satisfactorily in admixture with polished rice. Although the above described method is considerably good, it is not possible to ensure that all the brown rice treated even by this method is always of evenly good quality.
That is to say, in some cases too many fissures are formed, but in other cases fissures are insufficient. And further, treatment using the same conditions in the temperature, heating time, etc. of the hot air resulted in brown rice that differed in quality or in the mode of fissuring from lot to lot on account of the fact that the moisture, ingredients, properties of the bran layer, etc. of the brown rice varied depending on the kind, brand, place of production, year of production, and other characteristics of the brown rice used as raw material, so that the bran layer of the brown rice could not be made to develop fissures to a desired extent.
Thus, when the brown rice treated in quite the same manner is cooked under the same conditions, the cooked rice produced is uneven in hardness owing to the difference in the amount of moisture absorbed by the endosperm in each lot. Therefore, in order to make brown rice pleasantly palatable when cooked, though it may be cooked under almost the same conditions as in polished rice, the amount of the water added in cooking as well as the cooking time, etc. should all be varied according to the lot. Such a method is too unsatisfactory to be adapted for practical use.
The present inventors made an earnest investigation to develop a process for treating brown rice which can always make the bran layer of brown rice develop fissures to such an extent as desired irrespective of the variation in the kind, brand, etc. of the brown rice used as the raw material and which can prepare the brown rice such that it can always be readily cooked under the same conditions. As it was discovered that when the heat treatment for the brown rice is controlled by the quantity of heat energy absorbed by said brown rice, one can always produce treated brown rice of uniform quality whose bran layer has fissured to a desired extent, this invention was accomplished.